Silicone rubbers have hitherto been widely used in a variety of fields by exploiting their excellent heat resistance, cold resistance, electrical properties and other characteristics. In particular, given their good flow properties and their ability to invert, with good dimensional reproducibility, a fine pattern from a matrix, they have attracted attention as nanoimprint master materials, pad materials for printing on cured surfaces, blanket materials for offset printing and shape-forming materials for 3D printers. From the standpoint of dimensional reproducibility and workability in particular, frequent use has come to be made of addition reaction-curable liquid silicone rubber compositions. However, conventional addition-curable liquid silicone rubbers, which are used to invert a fine pattern by casting the uncured silicone rubber composition onto a matrix and then heat-curing the composition, have relied on the material and dimensional accuracy of the matrix.
Specifically, the matrix is generally created by a process that uses photolithography to form a fine pattern on a silicon wafer. However, because the largest silicon wafers available commercially today have a diameter of 300 mm, it has not been possible to produce plate materials for large microcontact prints of A4 size (210 mm×297 mm), for example.
Hence, to create the matrix, methods of forming a fine pattern with a resist material or the like on a glass substrate have been proposed, but the pattern accuracy has tended to be poor compared with a matrix produced on a silicon wafer using photolithography.
Silicone rubber compositions for use in making nanoimprint plate materials are generally supplied in the form of a composition containing an organopolysiloxane having a high degree of polymerization and a reinforcing resin. Such a composition is prepared by using a mixing device such as universal mixer or kneader to mix the reinforcing resin and various dispersants into a starting polymer. Addition-curable liquid silicone rubber compositions are typically cured by the application of heat, but the resulting silicone rubber composition and the silicone rubber which is the cured form thereof end up swelling or shrinking under the effect of heat. This has led to problems such as the inability to transfer or print patterns of prescribed dimensions, particularly in fine pattern inversion during the nanoprinting of photocurable resins, and also in pad materials used for printing on curved surfaces and blanket materials used in offset printing.
Acrylic-modified UV-curable silicone resins are sometimes used today in stereolithography. UV-curable silicone resins are generally free-radical crosslinked, and so one drawback has been inhibition of the cure by oxygen. Silicone compositions differ from other organic resins in that the high oxygen permeability distinctive to silicones gives rise to a cure-suppressing effect, ensuring storage stability when left open to the atmosphere.
However, because locally removing in a short time the oxygen diffused throughout the silicone resin is difficult, crosslinking in the UV-irradiated areas is unstable and interfaces between exposed areas and non-exposed areas after the cure are unstable, making fabrication at a high dimensional accuracy a challenge.
Moreover, in the case of layer-by-layer fabrication, unless light leakage from UV-irradiated sites is shielded with an ultraviolet absorber or a light-blocking pigment, the edges become indistinct. But, such shielding detracts from the inherent transparency of the silicone resin, limiting applications.
In UV-curable silicone resins, the addition-curing reaction is obtained using a platinum catalyst activated by exposure to UV radiation. The catalyst used has a high reactivity in the wavelength range of 200 to 400 nm, and light absorbance by the siloxane polymer serving as the base resin rises at a wavelength of about 250 nm. Generally, in stereolithography using acrylic or urethane-type UV-curable resins, when the g-line (436 nm) or shorter wavelength light is used as the light source, light leakage from the beam spot (the light-exposed region that forms on the liquid surface) is absorbed by the base resin, enabling sharp edges to form. However, in the case of UV-curable silicone resins such as acrylic-modified silicone resins, the base resin retains transmissivity even to the i-line (365 nm), and so light leakage from the beam spot is unavoidable, resulting in a lack of edge sharpness.
The following prior-art literature relates to this invention. Patent Document 1 (JP-A 2012-74644) discloses a plate material for microcontact printing which has a reduced content of low-molecular-weight siloxane, but a drawback is that mercapto-modified UV-curable silicone resins have a poor heat resistance. A system in which the cured form of a fluorinated polyether skeleton-containing fluororubber composition has been deposited as a layer over the surface of a silicone rubber composition (Patent Document 2: JP No. 5168510) undergoes thermal expansion under heating, making pattern transfer at a good dimensional accuracy difficult.
Patent Document 3 (JP No. 3417230) and Patent Document 4 (JP No. 4788863) disclose instances where acrylic-modified UV-curable silicone resins are used in stereolithography. However, because oxygen removal is not easy, after crosslinking of the irradiated areas or after curing of the exposed and non-exposed areas, the interfaces become unstable, making fabrication at a high dimensional accuracy difficult.